This invention relates in general to fluid actuators for causing movement of a piston relative to a cylinder. In particular, this invention relates to an air/oil intensifier type of fluid actuator having an improved structure for maintaining the separation of the air and oil within the intensifier cylinder.
Fluid actuators are well known devices which are adapted to generate mechanical movement in response to the application of pressurized fluid, such as air or oil. A basic fluid actuator includes a hollow cylinder having a piston slidably disposed therein. The outer circumferential surface of the piston slidably sealingly engages the inner circumferential surface of the cylinder so as to divide the interior of the cylinder into first and second chambers. When a pressurized fluid is supplied to the first chamber and the second chamber is vented, a pressure differential is created across the piston. This pressure differential causes the piston to slide relative to the cylinder in a first direction. Similarly, when a pressurized fluid is supplied to the second chamber and the first chamber is vented, the pressure differential created across the piston causes it to slide relative to the cylinder in a second direction. One or more fluid valves are usually used to control the supply of pressurized fluid to and the venting of the two chambers of the cylinder so as to effect movement of the piston in a desired manner.
Typically, a rod is connected to the piston for movement therewith. The rod extends outwardly from the cylinder into engagement with a workpiece. Thus, when the piston is moved within the cylinder as described above, the workpiece is moved therewith. The magnitude of the force which is generated against the workpiece is equal to the product of the pressure of the fluid in the chamber and the surface area of the piston exposed to that pressurized fluid. Thus, for example, if the magnitude of the pressurized fluid is one hundred pounds per square inch (p.s.i.) and the surface area of the piston is two square inches, then the magnitude of the force exerted by the piston against the workpiece will be two hundred pounds. Fluid actuators of this general type are commonly used in a variety of applications.
In some applications, however, the magnitude of the pressurized fluid available for use by the fluid actuator is limited. For example, in a typical manufacturing facility, pressurized air may be generated by a central supply system at a standard pressure, such as one hundred p.s.i., for the entire facility. At the same time, the magnitude of the force necessary for the fluid actuator to perform a given task may be relatively large, such as one thousand pounds. If a basic fluid actuator structure as described above were to be used to perform this task, the piston would have to very large (ten square inches in this example) in order to generate the necessary force. Obviously, it is undesirable from several standpoints to provide such a physically large piston.
To address the problem of generating relatively large forces using limited fluid pressures and relatively small pistons, it is known to modify the basic fluid actuator structure to generate an increased amount of force. These modified fluid actuator structures, which are commonly referred to as intensifiers, use multiple interacting pistons to multiply the forces produced by the pressurized fluid against the pistons, while maintaining relatively small sizes for the pistons. A typical intensifier structure includes a cylinder which is divided by an internal manifold into two working areas. In the first working area, a first piston is provided which divides the interior thereof into first and second chambers. A rod extends from the first piston through the manifold into the second working area. In the second working area, a second piston is provided which divides the interior thereof into first and second chambers.
When pressurized fluid is supplied to the first chamber of the first working area, a first force is generated against the first piston as described above. Movement of the first piston causes corresponding movement of the first rod in the first chamber of the second working area. The first chamber of the second working area is typically filled with a relatively incompressible liquid, such as oil. Thus, a second force is generated against the second piston because of the movement of the rod. The rod has a much smaller surface area than the first piston. Thus, the magnitude of the pressure generated in the first chamber of the second area against the second piston is multiplied relative to the original pressure exerted against the first piston. This multiplied pressure is applied against the surface area of the second piston and generates a multiplied force. A second rod connected to the second piston transmits the multiplied force to a workpiece.
The pistons within the intensifier maintain the separation of the air and oil. Seals are typically used around the pistons to prevent intermixing. The relatively high pressures created within the intensifier can cause a single seal to leak, undesirably allowing the air and oil to mix and reduce the efficiency of the intensifier. Dual seals having an intermediate air space are commonly used for separating the air and oil. It is preferable that the air gap should remain at atmospheric pressure throughout the entire piston stroke. A known method of maintaining atmospheric pressure in the air space is to vent the gap to atmosphere through a hole in the cylinder body located between the seals. To accomplish this, the vent hole must remain between the seals throughout the entire stroke of the piston. As a result, the seals must be separated by a sufficient distance to insure that neither seal will pass over the vent hole. Therefore, a relatively long piston must be used. It would be desirable to provide seal arrangement which seperates the air and oil within the intensifier cylinder by maintaining the pressure in an air gap between multiple seals at atmospheric pressure while using a shorter piston to decrease the size of the intensifier.